The invention relates to an adjusting device for a disc brake and, in particular, an adjusting device for a pneumatically actuated disc brake having a rotary-lever-actuated brake application device, which adjusting device can preferably be inserted into an adjusting spindle of the brake application device. The adjusting device has a clutch ring for coupling to a spring sleeve which is in engagement with the adjusting spindle.
Adjusting devices or wear adjustors for disc brakes exist in various embodiments. DE 10 2004 037 771 A1 (having U.S. published counterpart application US2009/209890 A1) discloses an adjusting device for a disc brake, the specifications of which are expressly incorporated by reference herein. This adjusting device is suitable for a pneumatically actuated disc brake, in particular one of sliding-caliper design. Furthermore, the adjusting device can however also be used in pneumatically actuated fixed-caliper or pivoting-caliper disc brakes.
Pneumatically actuated disc brakes have over time become standard equipment on heavy commercial vehicles. Such disc brakes require mechanical boosting or “force amplification” in order to produce the demanded brake application force, because the force of the pneumatically charged brake cylinders is restricted on account of the pressure level (at present approximately 10 bar) and the limited structural size of the brake cylinder. Presently known pneumatically actuated disc brakes have boost ratios of between 10:1 and 20:1. The piston strokes of the brake cylinders are in the range from 50 mm to 75 mm, resulting in brake application travels of approximately 4 mm for pressing the brake pads against the brake disc.
The friction material thickness of the brake pads lies in the range of 20 mm, and because two pads are installed, this results in a wear travel of approximately 40 mm, not taking disc wear into consideration. This travel is a multiple greater than the above-mentioned brake application travel. It is therefore necessary for the brake to be adjusted correspondingly to the pad wear by means of a device. The prior art provides automatic wear adjustment by means of which the so-called air play, that is to say the gap between the brake pads and the brake disc in the non-actuated state, is kept constant independently of the wear state and wear behavior of the brake pads.
In commercial vehicles, use is very often made of disc brakes which have an adjuster which is arranged concentrically in the cavity of a threaded spindle and which is driven eccentrically by a rotary lever via a drive element (for example shift finger or toothed wheel). During a braking process, the rotary lever which is coupled to the piston rod of the brake cylinder performs a rotational movement. Before the rotational movement of the lever is introduced into the adjuster via the coupling mechanism of the adjusting means (for example shift fork and shift finger or toothed wheel), a so-called idle travel must be overcome. This travel is decisive of the size of the so-called air play, because during this movement, the adjustment is not activated, and the brake application travel therefore constitutes the air play. After the idle travel is overcome, the adjuster is set in a rotational movement, and an adjusting process is initiated by the coupling to the threaded spindle or tube.
DE 10 2004 037 711 A1 describes an adjuster of this type, which is shown in FIG. 12. The adjuster is composed substantially of the following functional elements: shaft 2; bearing disc 3; axial bearing 5; collar bush, or spacer sleeve 19; shift fork, or drive ring 6; ball ramp clutch 7; cone clutch 17; and cylindrical spring 12. With regard to the description, reference is made to DE 10 2004 037 711 A1.
The adjusting device must basically perform two functions:
1. the automatic air play adjustment; and
2. the manual restoration or retraction of the adjusting mechanism upon replacement of the brake pads.
When installing new brake pads, thrust pieces which press the pads against the brake disc must be reset. This is carried out by turning back or retracting threaded plungers (threaded tubes or adjusting spindles) which, during use of the brake, have been screwed out by the automatically operating adjusting device according to pad wear.
When turning back the adjusting spindles, it must be ensured that the spindles are not turned against a delimitation with too high a force. If this were to occur, there is the risk of the adjustment being inoperative after replacing the brake pads because the force with which the adjusting spindles are jammed against the delimitation is greater than the adjusting force generated by the adjuster.
As mentioned above, when installing new brake pads, the adjusting spindles are reset by manually turning the adjuster. Since it is not possible to visually check the end position of the adjusting spindles, a mechanical, clearly perceptible turn-back delimitation is required.
It is therefore the object of the present invention to provide an adjusting device with a turn-back delimitation, with the above disadvantages being eliminated or significantly reduced, and further advantages being obtained.
This and other objects are achieved by an adjusting device for adjusting for wear of the brake pads and the brake disc of a pneumatically actuated disc brake having a rotary-lever-actuated brake application device, which adjusting device can preferably be inserted into an adjusting spindle. The adjusting device has a clutch ring for coupling to a spring sleeve which is in engagement with the adjusting spindle. A blocking device is arranged between the adjusting device, which can be inserted into the adjusting spindle, and the adjusting spindle. The blocking device forms a stop in the tangential direction relative to the direction of rotation for the adjusting spindle. In this way, it is advantageously obtained that, during the resetting of the adjusting spindle by the adjusting device, the adjusting spindle is prevented by the blocking device from becoming jammed, because the stop in the tangential direction halts the rotational movement.
Since the turning back of the adjusting spindle is carried out by use of the adjusting device, and the adjuster or the adjusting device is in direct engagement with the adjusting spindle, the turn-back delimitation can be realized by way of the adjuster, such that no complex modifications are necessary.
When the adjusting spindle has reached the pad installation position, the adjuster is retracted into the adjusting spindle to a maximum extent. The adjusting spindle performs a rotational movement relative to the clutch ring of the adjuster. A deformable or displaceable profiled blocking element is arranged between the end side of the adjusting spindle and the adjuster. The clutch ring of the adjuster preferably has a corresponding, for example a sawtooth-like crown, toothing adapted to the blocking element.
If the adjusting spindle is now turned back, it comes into contact with the blocking element at the end of the adjustment path. The blocking element is deformed or displaced axially by the end side of the adjusting spindle until the profile engages in the toothing of the clutch ring. Since the clutch ring is fixed to the disc brake, for example to the brake caliper thereof, by means of a collar bush and a bearing disc of the adjuster, the adjusting spindle can be turned back no further. A turn-back stop which acts in the circumferential direction is thereby realized. Jamming of the adjusting spindle can thereby be prevented. When the brake is actuated, the adjusting spindle can be turned away from the stop by the adjuster without the need to overcome a high friction force or jamming force.
An alternative embodiment provides a crown toothing on the adjusting spindle. Here, when the pad installation position is reached, the adjusting spindle engages with the end-side toothing directly into the end-side toothing of the clutch ring on the adjuster. As a result, the adjusting spindle can be turned back no further. Since it is the case in this solution too that the stop acts in the tangential direction, no jamming occurs. It is therefore possible for the adjusting spindle to be turned away from the stop with little force expenditure. The automatic adjustment function is thereby ensured without restriction.
Axial mobility of the blocking element is made possible for example by means of at least one lug which engages with a recess of the spring sleeve. The blocking element may have resilient hooks which are provided to engage with corresponding recesses of the clutch ring.
A disc brake, in particular a pneumatically actuated disc brake, has the above-described adjusting device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.